Colors are also prominent in the image of globular star cluster Omega Centauri, which contains almost 10 million stars, but the color contrast here is real. The gold dots are stars like our sun, but the blue ones are extremely hot, while the red ones are cool, O'Connell said.

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"Just by looking at the color of the stars in the picture, you can sort them by temperature and evolutionary state because the temperature differences here are caused by differences in the internal structure of these stars and in the kinds of fuels they're burning deep inside of them," O'Connell said.

Another image shows Stephan's Quintet, a group of five galaxies -- some of which are 290 million light-years away in the constellation Pegasus. Over time, those galaxies will eventually merge into a single big galaxy, O'Connell said.

Finally, images of a stellar nursery as seen in visible and infrared light reveal the secrets inside the Carina Nebula, located 7,500 light-years away.

"This is a cloud of dense material which is being bombarded by intense radiation from surrounding stars," O'Connell said.

"But dissolve to infrared and the cloud disappears. ... An energetic infant star is being formed inside this cloud."

Hubble is expected to continue its mission for at least five more years.